Why can't I open pdf's in Firefox?
- Did you recently upgrade to Acrobat 7? I had the same problem, and I was finally able to solve it this way (this assumes you are running Windows):
Go to c:\Program Files\Adobe\Acrobat 7.0\Reader\Browser (or whatever the corresponding path is on your computer)
Copy it into your Firefox plugins folder, which is probably at c:\Program Files\Mozilla Firefox\plugins. (There might already be a copy there; if so, this is the old version, so go ahead and overwrite it with the version you copied from the Acrobat 7 folder.)
This fixed the problem for me, and hopefully it will for you too.
Have you disabled any of Reader's plugins (normally done as a speed tweak). Other things to check would be about:plugins, and to check Tools>Options>Downloads>View & Edit Actions.